Method for the thermochemical cleaning and/or stripping of turbine components

ABSTRACT

The invention relates to a process for the thermochemical cleaning and/or stripping of turbine components, in particular engine components, with the steps: Production of a first gaseous mixture containing HF and H 2  in which the part by volume of HF in the mixture of HF and H 2  is in the range of 2.5 to 45% by volume, and application of the first gaseous mixture containing HF and H 2  on and/or in a turbine component for cleaning and/or stripping this turbine component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase application submitted under 35 U.S.C. §371 of Patent Cooperation Treaty application serial no. PCT/DE2009/000228, filed 19 Feb. 2009, and entitled METHOD FOR THE THERMOCHEMICAL CLEANING AND/OR STRIPPING OF TURBINE COMPONENTS, which application claims priority to German patent application serial no. 10 2008 011 747.1, filed 28 Feb. 2008, and entitled VERFAHREN ZUM THERMOCHEMISCHEN REINIGEN UND/ODER STRIPPEN VON TURBINENBAUTEILEN.

Patent Cooperation Treaty application serial no. PCT/DE2009/000228, published as WO/2009/106044, and German patent application serial no. 10 2008 011 747.1, are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a process for the thermochemical cleaning and/or stripping of turbine components, in particular of engine components.

BACKGROUND

U.S. Pat. No. 5,898,994 teaches using a mixture of HF gas and hydrogen in which the HF gas is in the range of 10-15% by weight, in particular in the range of 13% by weight and the remainder is hydrogen, in particular 87% by weight hydrogen for the removal of products produced by hot gas corrosion, such as metallic sulfides.

U.S. Pat. No. 5,728,227 teaches a process for stripping gas turbine components in which a section of the gas turbine component is exposed to a reduction gas containing more that 6% by weight halogen gas at a temperature above 1600° F.

U.S. Pat. No. 5,373,986 teaches a process for cleaning fissures in turbine components in which a tape is adhered over the fissure.

It is the purpose of the invention to make a process available by means of which turbine components can be cleaned and/or stripped in a simple manner.

SUMMARY AND DETAILED DESCRIPTION

Processes according to the invention are described and claimed herein. Preferred further developments are subject matter of the subclaims.

The process in accordance with one aspect provides for the thermochemical cleaning and/or stripping of turbine components, in particular engine components, that at first a first gaseous mixture is produced containing HF and H₂. It can be provided that this first gaseous mixture consists of HF and H₂. The first gaseous mixture is such that the part by volume of HF in the mixture of HF and H₂ is in the range of 2.5 to 45% by volume. Subsequently, the first gaseous mixture, that comprises HF and H₂, is applied on and/or in a turbine component for cleaning or stripping this turbine component. In an advantageous embodiment the part by volume of HF in the mixture of HF and H₂ is in the range of 5 to 25% by volume, preferably between 10 and 20% by volume. In an advantageous embodiment the turbine component is washed after the production and application of the first gaseous mixture on this turbine component. Such a washing can take place, e.g., by a second gaseous mixture or by a second gaseous substance.

For the sake of simplification the term second gaseous mixture is used but it should be noted that a second gaseous substance can also be used instead of it. The second gaseous mixture can be, for example, H₂. It can also be provided that the second gaseous mixture is a mixture of HF and H₂ in which the part by volume of HF in the mixture of HF and H₂ is in the range of 0.5 to 5% by volume, preferably in the range of 0.5 to 4% by volume, preferably in the range of 1 to 3% by volume. The second gaseous mixture is preferably produced and applied on the turbine component. It can be provided that a first gaseous mixture is repeatedly produced and applied on the turbine component and then a second gaseous mixture is subsequently produced and applied on the turbine component. This producing and applying of a first and the second gaseous mixture can be multiply repeated in an alternating manner for cleaning and/or stripping the turbine component. It can be provided that the pressure of the first gaseous mixture is varied over time. It can also be provided that the pressure of the second gaseous mixture is varied over time.

Furthermore, it can be provided that the first gaseous mixture is applied with a different pressure than the second gaseous mixture. The pressure of the second gaseous mixture can be lower than that of the first gaseous mixture. It can also be provided that the pressure of the second gaseous mixture is greater than that of the first gaseous mixture.

An advantageous embodiment provides that the pressure is varied in such a manner that it is present partially in the range of a subpressure and partially in the range of an overpressure. It can be provided that pressure changes take place in steps or that pressure changes take place continuously. It can also be provided that pressure changes take place solely in the overpressure range or that pressure changes take place solely in the subpressure range.

It can be provided that the pressure permanently changes during the entire process. However, it can also be provided that the pressure is constant at least at times.

The process is carried out in an advantageous embodiment in a closed system or in a closed container.

An especially preferred embodiment provides that the first or the second gaseous mixture is supplied and that a chemical reaction is brought about by this first and/or second gaseous mixture in the container that brings about a cleaning and/or stripping of the turbine component, and that the reaction products are subsequently removed partially or completely from the container.

This can take place in such a manner that the cited chemical reaction is brought about in particular by the first gaseous mixture and that the reaction products are subsequently removed out of the container by the second gaseous mixture.

An especially preferred embodiment provides that the turbine component is a hollow component. It can be provided, for example, that the inside surface of such a hollow component is cleaned and/or stripped by the process of the invention. The component can be, for example, a blade, in particular a compressor blade or turbine blade. The component is preferably a hollow blade, in particular a hollow turbine blade.

It is provided in an especially preferred manner that the thermochemical process in accordance with the invention for cleaning inside surfaces of hollow turbine components or service-conditioned damage by hot gas corrosion is carried out by a controlled thermochemical gas phase process at high temperatures.

It can be provided that the process has different periods or time sections in which time sections or periods can be present with high parts by volume of hydrogen fluoride (HF) of 2.5 to 45% in hydrogen-containing reaction atmosphere, followed by process sections with substantially hydrogen-containing reaction atmosphere.

The process of the invention is used especially preferably to remove metal oxides from the casting- and production process of the components before the coating with Pt, Pd, Zr, HF, Y, Al, Cr, Si and to remove metal oxide compounds and/or metal sulfur compounds and/or cover layers, in particular ceramics/oxide cover layers, and/or thermal insulation layers, in particular ZrO₂ thermal insulation layers in the case of coated components.

It can be provided that the turbine components on which the process of the invention is used consist of nickel-based alloys and/or cobalt-based alloys that are used or can be used, e.g., in the hot areas of airplane turbines and gas turbines. Such components and turbines often have small wall thicknesses and have, especially when they are cooled with air during use, inside cooling surfaces and cooling fits.

The Ni/Co super alloys for gas turbines are frequently optimized for the best possible combination of temperature resistance, creeping strength and expansion change capacitance. Such a component can be used, for example, in the process of the invention.

This can take place, for example, by the selection of suitable alloy elements or also by the use of high-quality castings that are solidified in a directed manner or solidified in a monocrystalline manner.

Such measures for increasing the strength such as, e.g., Cr reduction in the base material and limitation of the Al- and/or Ti content can, however, result in a limited service life as regards oxidation and corrosion. In order to improve the resistance to oxidation and corrosion, the components can be diffusion-coated with Al, PtAl, Cr, or Si or be coated with MeCrAlY support layers. This can take place, for example, in the framework of the manufacturing of new parts but also in the framework of the overhauling of already coated parts.

In an advantageous embodiment inside surfaces and/or outside surfaces of turbine components, in particular turbine blades, can be cleaned with the process in accordance with the invention for being prepared for the coating in the thermochemical process.

It is provided in an especially preferred manner that during the process in accordance with the invention a pressure fluctuation of Δp>5 mbar and Δp<200 mbar is given. For example, a pressure fluctuation can be present during the process that is in the range between 20 and 60 mbar. It can also be provided that a pressure fluctuation is present that corresponds substantially to 30 mbar.

The process can take pace with a high flow of >5 volume elements exchange rate per hour.

This means in particular that per hour at least five times the container volume is introduced into the container and removed from it.

It can be provided that the HF components vary in time. This can be controlled, for example, by the addition of H₂. It can also be provided in particular that fissures are cleaned by the process of the invention.

The container in which the process can be carried out can have a volume, for example, that >0.3 m³ and <10 m³. For example, it can be provided that the container volume is in the range of 0.5 to 5 m³, preferably between 0.5 and 3 m³, especially preferably between 1 and 2 m³, especially preferably substantially 1.5 m³. In an especially preferred embodiment a thorough washing always takes place during the process of the invention, i.e., a gaseous mixture is supplied and reaction points are removed. For example, it can be provided that the following reaction is carried out during the process of the invention:

6×HF+Al₂O₃→2 AlF₃+3 H₂ O.

The cycle time ΔT can be, for example, in the range of 10 sec. to 10 min. It can be provided that the pressures and/or the mixing ratio of the gaseous mixture is/are changed during the process. 

1-10. (canceled)
 11. A method for the thermochemical cleaning and/or stripping of turbine components, in particular of engine components, the method comprising the following steps: production of a first gaseous mixture containing HF and H₂ in which the part by volume of HF in the mixture of HF and H₂ is in the range of 2.5 to 45% by volume; application of the first gaseous mixture containing HF and H₂ on and/or in a turbine component for cleaning and/or stripping this turbine component; and washing of the turbine component after the production and application of the first gaseous mixture on the turbine component by application of a second gaseous mixture or substance on and/or in the turbine component; wherein the second gaseous mixture or substance contains HF and H₂ and the amount of HF in the mixture or substance of HF and H₂ measured in % by volume is less than in the first gaseous mixture.
 12. The method according to claim 11, wherein the part by volume of HF in the first gaseous mixture of HF and H₂ is in the range of 5 to 25% by volume.
 13. The method according to claim 11, wherein the second gaseous mixture or substance contains HF and H₂ and the amount of HF in the mixture or substance is in the range of 0.5 to 5% by volume.
 14. The method according to claim 11, wherein the first gaseous mixture and the second gaseous mixture or substance are applied on and/or in the turbine component in a multiply alternating manner.
 15. The method according to claim 11, wherein the pressure of at least one of the first gaseous mixture and the second gaseous mixture or substance is varied over time.
 16. The method according to claim 11, wherein the method is carried out in one of a container and a closed system.
 17. The method according to claim 16, wherein at least one of the first gaseous mixture and the second gaseous mixture or substance is supplied to the container and a chemical reaction is brought about by the first gaseous mixture and/or second gaseous mixture in the container that brings about a cleaning and/or stripping of the turbine component, and that the reaction products are subsequently removed partially or completely from the container.
 18. A method for the thermochemical cleaning/stripping of a component having unwanted material thereon, the method comprising the following steps: (a) applying a first gaseous substance containing HF and H₂ to the component to be cleaned/stripped, the first gaseous substance including a % by volume of HF in the range of 2.5 to 45% by volume; (b) facilitating a reaction between the HF in the first gaseous substance and at least a portion of the unwanted material on the component such that at least a portion of the unwanted material is converted to a reaction product; (c) applying a second gaseous substance containing HF and H₂ to the component to be cleaned/stripped, the second gaseous substance including a % by volume of HF that is less than the % by volume of HF in the first gaseous substance, whereby at least a portion of at least one of the first gaseous substance and the reaction product is washed from the component; and (d) repeating steps (a)-(c) until a desired amount of the unwanted material is cleaned/stripped from the component.
 19. The method according to claim 18, wherein the component is disposed within a container having a volume and the first and second gaseous substances are successively introduced and removed from within the container.
 20. The method according to claim 19, wherein the step of applying a second gaseous substance (step (c)) further comprises removing the reaction products from the container with the second gaseous substance.
 21. The method according to claim 19, wherein the volume of first and second gaseous substances introduced and subsequently removed from the container during each hour is greater than 5 times the volume of the container.
 22. The method according to claim 18, wherein the component includes a hollow portion having a volume connected to a closed system and the first and second gaseous substances are successively introduced and removed from the closed system to the hollow portion of the component.
 23. The method according to claim 22, wherein the step of applying a second gaseous substance (step (c)) further comprises removing the reaction products from the hollow portion of the component with the second gaseous substance.
 24. The method according to claim 22, wherein the volume of first and second gaseous substances introduced and subsequently removed from the hollow portion of the component during each hour is greater than 5 times the volume of the hollow portion.
 25. The method according to claim 18, wherein the step of facilitating a reaction (step (b)) further includes varying the pressure of the first gaseous substance over time.
 26. The method according to claim 25, wherein the pressure fluctuations Δp of the first gaseous substance is within the range of Δp>5 mbar to Δp<200 mbar.
 27. The method according to claim 25, wherein the step of applying a second gaseous substance (step (c)) further comprises varying the pressure of the second gaseous substance over time.
 28. The method according to claim 27, wherein the pressure fluctuations Δp of the second gaseous susbstance is within the range of Δp>5 mbar to Δp<200 mbar.
 29. A method for the thermochemical cleaning/stripping of a component having unwanted material thereon, the method comprising the following steps: (a) providing a container having a volume; (b) positioning the component within the container; (c) introducing a first gaseous substance containing HF and H₂ into the container surrounding the component, the first gaseous substance including a % by volume of HF in the range of 2.5 to 45% by volume; (d) varying the pressure of the first gaseous substance in the container with pressure fluctuations Δp within the range of Δp>5 mbar to Δp<200 mbar until a reaction between the HF in the first gaseous substance and at least a portion of the unwanted material on the component such that at least a portion of the unwanted material is converted to a reaction product; (e) introducing a second gaseous substance containing HF and H₂ into the container surrounding the component, the second gaseous substance including a % by volume of HF that is less than the % by volume of HF in the first gaseous substance, whereby at least a portion of at least one of the first gaseous substance and the reaction product is washed from the component; (f) removing at least a portion of the reaction products from the container; and (g) repeating steps (a)-(f) until a desired amount of the unwanted material is cleaned/stripped from the component.
 30. The method according to claim 29, wherein the step of introducing a second gaseous substance (step (e)) further comprises varying the pressure of the second gaseous substance in the container with pressure fluctuations Δp within the range of Δp>5 mbar to Δp<200 mbar. 